Generally, as shown in FIG. 1, the conventional glass sheet chamfering apparatus which includes vacuum absorption devices is constituted such that a rotary table 3 is installed by securing a vertical pole 2 on the top of a body 1 in which an absorption pump is accommodated; a plurality of absorption devices 5 are installed on the rotary table 3 in such a manner that they should communicate with the absorption pump; a glass sheet 6 to be chamfered is mounted on the tops of the absorption devices 5 before the absorption pump is activated to vacuum-absorb the glass sheet 6; and a diamond wheel 4 which is disposed at a side of the body 1 is adjusted to the required bevel angle so that the glass sheet 6 can be ground. As shown in FIG. 2A, an O-ring 16 is secured on the top of a cylindrical body 10' of the absorption device 5 conventionally, and then, the glass sheet 6 is mounted on the O-ring in such a manner that the inside of the O-ring should be sealed off with respect to the outside, thereafter the absorption pump being activated to absorption-secure the glass sheet.
When such an absorption device 5 is used for a long time, the O-ring 16 is worn out or contracted due to the continuous contact of the O-ring 16 with the glass sheet 6, with the result that small gaps are generated between the O-ring 16 and the glass sheet 6. In turn, this brings the consequence that glass powders and diamond wheel powders produced during the chamfering are introduced into the cooling fluid to be absorbed into the absorption pump, with the result that the cylinder is worn off or corroded. This again brings the result that the performance of the pump is deteriorated or the life expectancy of the pump is shortened. Further, the horizontal posture of the glass sheet is distorted, and the edge of the glass sheet is chamfered with an irregular form, thereby degrading the commerical merit of the products. Still further, in the case where a glass sheet having a size smaller than the extent of disposition of the absorption devices on the rotary table is to be chamfered, the suction holes 10' a of the cylindrical body 10' of some of the absorption devices 5 are open, so that they have to be closed with separate closures.
In order to overcome these problems, a measure have been attempted recently as described below. That is, as shown in FIG. 2B, an actuation rod 17 having a diameter smaller than that of the suction hole 10' a and provided with an internal packing 19 is installed by means of a spring within the interior of the cylindrical body 10' of the absorption device 5, in such a manner that the leading end of the actuation rod should be located higher than the O-ring 16. Thus, the packing 19 is let to close the suction hole 10' a through the elastic force of the spring 18, while, upon mounting of the glass sheet 6, the actuation rod 17 is lowered due to the gravity of the glass sheet, and at the same time, the glass sheet 6 is adhered on the O-ring 16.
However, in this method also, the suction hole 10' a is open throughout the chamfering process, and therefore, the introduction of the foreign materials can not be absolutely prevented.